In physics and engineering, the quality factor (or “Q-factor”) of an oscillating system is a dimensionless parameter that compares a time constant for amplitude decay to oscillation period. Equivalently, the Q-factor compares the frequency at which the system oscillates to the rate at which it dissipates its energy. For example, a pendulum oscillating in air would have a high-Q factor, while a pendulum oscillating in oil would have a low-Q factor.
In electronics, when a resonant filter is driven by a sinusoidal signal, its resonant behavior depends strongly on its Q-factor. Resonant filters respond to frequencies close to their resonant frequency more strongly than they respond to non-resonant frequencies, and their response falls off more rapidly as the driving frequency moves away from resonance. Thus, a radio receiver with a high-Q factor filter in its signal path is difficult to tune when compared to a low-Q factor filter, but once tuned does a better job of filtering out other nearby and far-off frequencies.
Whenever the achievable Q-factor is limited due to technology constraints, it can be increased by means of special circuits—namely Q-enhancement or loss compensation circuits. Usually, the employment of these circuits leads to extra power consumption.
As will be appreciated from the above discussion and embodiments described herein, there is an on-going need for circuits that provide a good blend between ease of tuning, good filtering characteristics, and power consumption.